APPENDIX. 187 



by stronger (70$), which should be changed once or twice at inter- 

 vals of a few hours; they are finally placed in 90$ alcohol, which 

 should be liberally used. The trouble demanded by this method 

 will be fully repaid by the results; and well-preserved specimens 

 are in some respects better than fresh. They should be quite 

 straight, fully extended, and plump, and they may be used either 

 for dissection or for microscopic study. 



For the purposes of section-cutting worms should be carefully 

 washed and placed in a moist vessel containing plenty of wet filter- 

 paper torn into shreds. The worms will devour the paper, which 

 should be changed several times until the paper is voided perfectly 

 clean.* The worms are then preserved in the ordinary way, and 

 when properly hardened are cut into short pieces, stained with 

 borax-carmine, imbedded in paraffin, and cut into sections with 

 the microtome. 



The embryological development is very difficult to study. In 

 the latitude of Philadelphia egg-capsules may be found in great 

 numbers in old manure-heaps in May and June. One end of the 

 capsule should be sliced off with a very sharp scalpel and the con- 

 tents drawn out, under water, with a large-mouthed pipette. The 

 mass may then be mounted in water under a supported cover-glass, 

 and studied with the microscope. The embryos may be preserved 

 in Perenyi's Fluid, and either studied whole in the preserving fluid 

 or hardened in alcohol and cut into series of sections. 



* This method of freeing the alimentary canal from earth and sand was 

 suggested by Professor Benjamin Sharp. 



